In the present case, the term “adjustment element” is to be understood to be all-encompassing. Said term covers tailgates, trunk lids, engine hoods, doors, in particular side doors, luggage compartment floors or the like, of a motor vehicle.
However, the drive arrangement under discussion is primarily used in tailgates and side doors in motor vehicles. It is used for the motorized adjustment of the respective adjustment element in the closing direction and in the opening direction. It is generally important in this case that the drive arrangement also permits manual adjustment operation, in addition to motorized adjustment operation. Manual adjustment operation is important particularly in the event of an emergency, for example in the event of a crash or in the event of a power failure.
A known drive arrangement (DE 20 2005 007 155 U1) is associated with a tailgate. The drive arrangement is equipped with two spindle drives which, in each case in a compact structural unit, have a drive motor, an intermediate gear mechanism with a clutch, and a spindle/spindle nut mechanism. A spring arrangement which counteracts the weight force of the associated tailgate is provided in the respective structural unit. The drive arrangement further has a drive control means which is used to actuate the two drives, in particular the two drive motors. The drives are equipped in a non-self-locking manner, and therefore manual operation can be realized in a simple manner.
The described drive arrangement can be used for the motorized adjustment of tailgates of considerable size and/or substantial weight. This creates new degrees of freedom when designing tailgates of this kind. However, the increase in weight is, in principle, also associated with an increased risk in the event of a failure of the drive components. For example, in the event of a fracture in the above spring arrangement, it is necessary to ensure that the tailgate does not drop in the closing direction in an unbraked manner due to gravity.
In the case of the known drive arrangement (WO 2010/083999 A1) on which the invention is based, an overvoltage protection means of the drive control means is used for the purpose of braking the drive in the event of a non-motorized adjustment of the adjustment element above the adjustment speed for normal operation in the short-circuit mode. In this case, the drive control means is equipped with a driver unit for supplying electrical drive power to the drive, said driver unit having a conventional H-bridge circuit.
In the case of the known drive arrangement, use is made of the fact that the drive motor operates as a generator in the event of a non-motorized adjustment and generates a generator voltage by means of which the overvoltage protection means of the drive control means can be triggered. Triggering of the overvoltage protection means leads in this case to short-circuiting of the respective drive motor, this leading to corresponding braking of the drive motor.
In the known drive arrangement, it is advantageous that rapid and heavy braking of the drive in the event of an emergency using simple means, and therefore a high level of operational reliability, are ensured. However, in the case of some applications, moderate braking would be desirable, and this would be perceived by the user as an increase in comfort.
The invention is based on the problem of designing and developing the known drive arrangement in such a way that the comfort of use is increased while the operational reliability is maintained.